Comparative evaluation of acoustic techniques for detection of damages in historical wood

This study assesses the suitability and sensitivity of select acoustic devices (Arborsonic Decay Detector, Fakopp Ultrasonic Timer with two types of sensors–TD45 and US10, and Fakopp 2D) for identification of damage in seven approximately 315 year old fir joining beams acquired during the reconstruction of the Baroque truss in the St. Mary of the Assumption Church in Vranov nad Dyjí, Czech Republic. The particular acoustic devices did not always provide similar results. However, brown rot and other inner damages in fir beams, located closer to their endings situated on masonry and connected with rafters, were determined with all acoustic devices. The possibility of indirect prediction of the strength, elasticity and hardness of the historical wood by means of the acoustic method was verified by correlation analyses, however, not seldom without higher significance. Generally, the results obtained indicate that it is not possible to fully rely on in situ acoustic methods for inspection of defects in wooden elements of historical structures, and therefore they should be combined with visual inspection and some other instrumental method(s).